This invention relates to an electronic network utilized to compensate for nonlinear phase distortion created by other networks and circuitry. Such nonlinear phase distortion is typically created by networks such as filters, amplifiers, amplitude equalizers, FM modulators, FM demodulators and other analog and digital broadband communications devices.
Envelope delay distortion or group delay distortion has previously been corrected utilizing various networks such as different bridge T configurations derived from an allpass lattice structure. Reflective type equalizers, such as 90.degree. hybrids and 180.degree. hybrids have also been utilized. However, conventional equalizer networks have shared a common disadvantage: as the shape factor increases (greater envelope delay correction per unit of frequency bandwidth), the networks exhibit greater amplitude distortion due to the finite Q of the reactive elements used in implementation of the networks. Thus, while correcting for envelope delay distortion, a second distortion is introduced, which is amplitude distortion versus frequency.
Methods for measuring envelope delay are disclosed in U.S. Pat. No. 3,400,329 to Cannon together with amplitude and delay distortion correcting networks comprising cascaded frequency selective active corrective networks which separately correct a portion of the frequency band to be corrected. U.S. Pat. No. 4,258,340 to Ryu discloses an amplitude equalizer intended to have flat delay distortion characteristics comprising a pair of amplitude equalizers having complimentary, and thus cancelling, delay distortion characteristics. Such equalizers include delay circuits and/or phase shifters but do not teach or suggest correction of envelope delay distortion while avoiding amplitude distortion.
U.S. Pat. No. 4,333,063 to Ryu et al. discloses another amplitude equalizer for use within a predetermined frequency band, which equalizer is intended to exhibit no delay distortion. It utilizes combinations of signal splitters, delay circuitry and polarity and gain adjusting means. Additionally, U.S. Pat. No. 4,352,190 to Hullwegen discloses an automatic equalizer for data transmission and suggests a delay equalizer which includes an output amplitude stabilizer utilizing active network elements.
None of this art, however, or other art known to applicant discloses the simple and effective variable amplitude delay equalizer of the present invention.